DESCRIPTION (From the applicant's abstract): The long term goals of the project are aimed at determining fundamental roles of chemokines and their receptors in central nervous system (CNS) function. Chemokines are a group of structurally related cytokines that exhibit pleiotropic actions on a wide variety of cells but whose function has been largely characterized as regulators of peripheral leukocyte movement (i.e, chemotaxis) and activation. Receptors for chemokine peptides have been described and they are members of the seven transmembrane spanning, G-protein coupled receptor superfamily. Expression of chemokine receptors on pheripheral leukocytes is well documented; some of these receptors mediate, with CD4, entry of HIV-1. More recently, chemokines and their receptors have been demonstrated to be expressed by cells in the CNS, although this expression is often evident only in neuropathological situations. On the other hand, a unique cell surface-expressed chemokine ligand, term fractalkine, and its receptor CX3CR1, are constitutively expressed in non-pathological CNS. Utilizing in situ hybridization analysis, it has been determined that microglia express CX3CR1 mRNA, while neurons are the principle source of fractalkine mRNA in the rat CNS. In addition, the expression of this ligand:receptor pair is dynamically regulated in the injured rat facial motor nucleus (FMN) after peripheral nerve transection. These data prompt the overall hypothesis that chemokine-dependent signaling mechanisms mediate unique neuronal-glial cells interactions under normal and injury/repair states of the CNS. Experiments proposed herein will ultimately provide insights into the role of fractalkine and CX3CR1 in CNS function. The specific aims will: 1. map sites of expression of fractalkine and CX3CR1 protein in the CNS and determine their expression profiles in neuropathologies where neurons do NOT regenerate, e.g. neonatal facial nerve axotomy and rubrospinal tractotomy. 2. evaluate the microglial response and extent of neuronal regeneration in the adult FMN and red nucleus, after nerve transection (facial nerve axotomy or rubrospinal tractotomy, respectively), in mice deficient in either fractalkine or CX3CR1. 3. determine structural characteristics of fractalkine that are necessary for CX3CR1 activation. The research plan will utilize broad approaches that span in vitro and in vivo experimental paradigms. These studies are designed to fill large gaps in knowledge regarding the role of chemokine, and specfically fractalkine, dependent mechanisms in CNS function.